This invention relates generally to X-ray devices and in particular to energy switch assemblies and linear accelerators incorporating the same.
X-ray apparatuses such as linear accelerators are widely used in various applications including in medical radiation therapy and imaging. For example, accelerator guides are used to accelerate electron beams which can be directed to X-ray targets to produce radiation for treatment of diseases and imaging. To produce suitable radiation profiles for particular medical applications, it is necessary to vary the energy level of electron beams incident on an X-ray target.
Energy switches have been used with accelerator guides to modulate the energy levels of output electron beams. In use, a metallic probe is inserted into a side cavity of an accelerator guide to change the mode of the side-cavity coupling at the radio frequency of accelerating cavities downstream of the side cavity. At a predetermined probe insertion depth, a desirable mode-shape is developed, resulting in a field step. The result is an energy level of an output beam controlled by the position of the metallic probe. U.S. Pat. No. 7,339,320 discloses a standing wave particle beam accelerator and an energy switch, the disclosure of which is incorporated herein by reference in its entirety.
Conventional energy switches use pneumatically driven mechanisms to control a probe end at two positions, an inserted position and a retracted position. Thus, the energies of output beams controlled by conventional energy switches are limited to two levels, a first energy level with a probe end inserted in a switch side cavity and a second energy level with the probe end retracted out of the switch side cavity.
Conventional energy switches are typically assembled to accelerator guides after a final bake-out procedure since conventional energy switches cannot survive high bake-out temperatures. Bake-out is a process in which an accelerator guide assembly is heated to elevated temperatures for a period of time and internally evacuated to outgas vacuum components in the guide assembly. In assembling a conventional energy switch, it is necessary to reopen the vacuum of an accelerator guide assembly. As a result, the vacuum integrity and cleanliness of the accelerator guide assembly would be compromised.